| Pluto is out, and Zena and Ceres are in. Well, almost. | | | | other planets. |
| Now all three are out. | | | | 3. To be a planet a space object must dominate its |
| Recently, Michael Brown, an astronomer from Caltech, | | | | own orbit and clear its own area of other smaller |
| discovered what he thought was a new planet, which | | | | space objects. |
| he called Zena. He presented his findings and | | | | A "dwarf planet" was defined as a celestial body that |
| submitted his studies to the 26th General Assembly of | | | | is in an orbit around the Sun, has sufficient mass for its |
| the International Astronomical Union (IAU) who met last | | | | own gravitational forces to assume a hydrostatic |
| week, 20 - 26 August 2006 in Prague, Czechoslovakia | | | | equilibrium or "nearly round" shape, has not cleared its |
| to discuss this new discovery and to review the | | | | orbital neighborhood of other space objects, and it is |
| selection criteria for naming planets. Of the 2,700 | | | | not a satellite. |
| delegates who attended the meeting only 720 were | | | | The IAU also resolved that all other space objects, |
| still in attendance at the end of the week. Only about | | | | except satellites orbiting the Sun, shall be referred to |
| 400 delegates were on hand the final day but only a | | | | collectively as "Small Solar-System Bodies" |
| handful of members were eligible to vote on a revised | | | | The old mnemonic "My very energetic mother just |
| description of what constitutes a planet and Brown's | | | | served us nine pizzas", by which millions of people |
| studies were accepted. They added Zena to the | | | | learned to recite the planets, no longer applies. |
| roster of the Sun's planets (also knows as UB313, | | | | However, We do have a new one to help you |
| Zena is larger than Pluto). They also accepted a | | | | remember the planets in the new line up. |
| second nomination, Ceres. | | | | "My very Energetic Mother Just Served Us Noodles." |
| Then suddenly, in a direct reversal of their previous | | | | Here are some other, more original suggestions: |
| decisions the IAU decided that the long-standing | | | | "My very exhausted mother just sent us nachos" |
| member planet, Pluto, no longer met the criteria to be a | | | | "Make Very Extraordinary Meals of Jell-O, |
| planet. Pluto was demoted to space dust. The two | | | | Strawberries, and Unsalted Nuts." |
| other small solar system bodies nominated, Zena and | | | | Just in case you may have forgotten, the names of |
| Ceres, were then summarily rejected. | | | | the planets they are, listed in order of their distance |
| The IAU also redefined the three criteria necessary to | | | | from the Sun, Mercury, Venus, Earth, Mars, Jupiter, |
| qualify an object as a planet. | | | | Saturn, Uranus, Neptune, and the newly demoted |
| 1. A planet must be round in shape. What this means is | | | | "dwarf planet", Pluto. |
| that is planet must be large enough to have had its | | | | Try making up your own mnemonic and get the kids |
| mass pulled into a round shape as the result of its own | | | | involved, too. This could very easily be made a part of |
| gravitational forces. It was also suggested, but not | | | | one of your science lessons. But don't use Pluto, Zena, |
| made part of the definition, that a planet must be at | | | | or Ceres in your new mnemonic. At least not for now, |
| least 1000 kilometers in diameter. | | | | the IAU may change their minds at their next meeting |
| 2. Planets must have a defined, regular orbit around the | | | | in 2009. |
| Sun, and not be either stars themselves or satellites of | | | | |